1. Field of the Invention
The present invention relates to a light-absorptive antireflection film and a display device using the same, more particularly a light-absorptive antireflection film able to increase contrast and suitable for a cathode ray tube (CRT) or other display device using flat panel glass and a display device using the same as an antireflection film of the flat panel glass. Also, the present invention relates to a method of producing the above light-absorptive antireflection film and a display device.
2. Description of the Related Art
In recent years, progress has been made in flattening the outer surface of a face panel of a display device, for example, cathode ray tube. Generally, the face panel of a cathode ray tube is formed thicker at corner parts than at a center part so as to give implosion proofness. When the outer surface of the face panel of a cathode ray tube is flattened, the mechanical strength with respect to implosion of the cathode ray tube decreases compared with when the outer surface of the face panel is curved. Therefore, it is necessary to increase the difference of the panel thickness between the center part and the corner parts of the face panel so as to maintain the implosion-proofness of the cathode ray tube.
The contrast of a cathode ray tube is mainly determined by the light absorption of a panel glass and the reflectance of a phosphor screen with respect to outer light. In a conventional cathode ray tube, an increase of contrast has been sought by increasing the light absorption at the panel glass somewhat and decreasing the reflectance of the phosphor screen. However, along with flattening of the outer surface of the face panel, if a difference of transmittance arises corresponding to the difference of the panel thickness, the uniformity of the brightness deteriorates. Therefore, it becomes difficult to obtain optimum contrast at both the center and corner parts of the panel.
To deal with the above difficulty, the transmittance of the glass is made higher and absorbency of light is given to an antireflection film formed on the surface of the panel glass so as to make the total transmittance equal and obtain good contrast.
As this type of antireflection film, for example, a light-absorptive antireflection member having a two-layer structure of a light-absorptive film and a silica film and functions of prevention of reflection, absorbency of light, and electroconductivity (see Japanese Unexamined Patent Publication (Kokai) No. 9-156964) has been known. According to this light-absorptive antireflection member, the transmittance of the panel glass is increased for example from 50 percent to 80 percent, while the transmittance of the light-absorptive antireflection member in the visible light region is decreased for example from 80 percent to 50 percent. Due to this, even contrast is obtained when the transmittance of the panel glass is low and the transmittance of the light-absorptive antireflection member is high.
As a similar antireflection film, an electroconductive and light-attenuating antireflection coating film having a structure of glass/SnO2 (tin oxide)/TiN (titanium nitride)/SnO2/TiN/SiO2 (silicon dioxide) (see Japanese National Patent Publication (Kohyo) No. 6-510382) etc. have been known.
However, according to the light-absorptive antireflection member described in the above Japanese Unexamined Patent Publication (Kokai) No. 9-156964, it is necessary to increase the total thickness of the light-absorptive antireflection member so as to decrease the transmittance of the light-absorptive antireflection member. Therefore, when the difference of refractive index between the panel glass and the light-absorptive film is large, light incident from a glass side is reflected at an interface of the glass and the light-absorptive film and the reflected light is again reflected at the glass surface etc., whereby the problem of the image appearing double or a ghost is seen occurs.
For example, in the case of a cathode ray tube, since light emitted from the phosphor screen is reflected at the interface of the glass and the light-absorptive film and the reflected light is reflected again at the phosphor screen, the image appears double. Particularly, according to the light-absorptive antireflection member described in the above Japanese Unexamined Patent Publication (Kokai) No. 9-156964, since nitrides of titanium, zirconium, or hafnium are preferably used as the light-absorptive film, the difference of refractive index between the panel glass and the light-absorptive film is large and a ghost often becomes a problem.
On the other hand, in the electroconductive light-attenuating type antireflection coating film disclosed in Japanese National Patent Publication No. 6-510382, by optimizing the refractive index and thickness of the first layer transparent film from the glass side, it is possible to attenuate the incident light from the glass surface side, but there are many demerits due to the increase of film configuration. For example, due to the increase of the number of processes, the production cost increases. Also, it is very difficult to obtain the optimal material for a thin layer having absorbency in consideration of wavelength dispersion of an optical constant. For example, it is not possible to design the material in consideration of the ratio of emission spectra of R (red), G (green) and B (blue) of the cathode ray tube.
In addition to the above, as a structure formed on the surface of the panel glass for the purpose of improving the display quality of a cathode ray tube, many have been proposed which have functions of prevention of reflection, adjustment of the transmittance of light, improvement of contrast by adjustment of the dispersion of wavelength of the transmitted light, and decrease of spurious radiation by control of the surface resistivity.
For example, Japanese Unexamined Patent Publication (Kokai) No. 6-208003 discloses an antireflection film of a multilayer structure comprising at least one layer containing a dye. Japanese Unexamined Patent Publication No. 10-21858 discloses an antireflection film of a multilayer structure able to improve contrast and prevent static electricity by inclusion of fullerene. Japanese Unexamined Patent Publication No. 4-334853 discloses an antireflection multilayer film of a multilayer structure formed on a surface of panel glass having a transmittance of not more than 50 percent and containing a dye or pigment and electroconductive filler.
In these antireflection films, each layer configuring the antireflection film is formed by spin coating, dip coating, or other wet-coating. Therefore, sometimes sufficient uniformity of film quality and surface hardness cannot be obtained. Also, when an electroconductive filler is added for giving electroconductivity to the antireflection film, it is necessary to disperse the electroconductive filler at a high concentration for increasing the electroconductivity and the problems of aggregation of the electroconductive filler etc. occur.
As explained above, no antireflection film able to give a high effect in all of antireflection, improvement of contrast, and decrease of spurious radiation has been realized.
An object of the present invention is to provide a light-absorptive antireflection film having an antireflection function and electroconductivity able to improve contrast.
Another object of the present invention is to provide a display device improved in a display quality.
A still other object of the present invention is to provide methods of producing the above light-absorptive antireflection film or a display device using the same by a simple process and able to prevent an increase of the production cost.
According to a first aspect of the present invention, there is provided a light-absorptive antireflection filter allowing light incident from a first surface side to pass at a predetermined transmittance and attenuating reflected light of the incident light from a second surface side by interference of light at an antireflection multilayer film, said light-absorptive antireflection filter characterized by comprising a light-absorptive film formed on the first surface and containing pigment microparticles; the antireflection multilayer film formed on the second surface and contacting the light-absorptive film; and at least one electroconductive thin film included in the antireflection multilayer film.
Preferably, a physical thickness of the light-absorptive film is at least about the size of the pigment microparticles and set within a range wherein a quality of the light-absorptive film becomes uniform.
According to a second aspect of the present invention, there is provided a display device comprising a display unit displaying an image and a light-absorptive antireflection multilayer film formed on the display unit, allowing light incident from a first surface side of the display unit side to pass at a predetermined transmittance, and attenuating reflected light of the incident light from a second surface side; said light-absorptive antireflection multilayer film comprising a light-absorptive film formed on the first surface and containing pigment microparticles, an antireflection multilayer film formed on the second surface and contacting the light-absorptive film, and at least one electroconductive thin film included in the antireflection multilayer film.
Preferably, a surface of the display unit is substantially flat.
In the light-absorptive antireflection film and display device using the same of the above configuration, by making the light-absorptive film contain pigment microparticles and selecting a suitable type and blending ratio of pigment microparticles, it is possible to control a transmittance and wavelength dispersion of the transmittance freely. As a result, a selective absorption filter considering the RGB brightness of a display device can be achieved. Also, the antireflection multilayer film attenuating reflected light of the incident light by interference of light and decreases spurious radiation since at least one layer is comprised of an electroconductive thin film.
According to the light-absorptive antireflection film of the present invention, it is possible to prevent reflection and decrease spurious radiation and, further, it becomes easy to control the transmittance of the light-absorptive antireflection film.
According to the display device of the present invention, it is possible to prevent reflection of a display unit and decrease spurious radiation and, further, it becomes possible to obtain a high contrast.
According to a third aspect of the present invention, there is provided a method of producing a light-absorptive antireflection film of the present invention comprising the steps of coating a solution containing pigment microparticles and a solvent; drying off the solvent to form a light-absorptive film containing the pigment microparticles and having a predetermined transmittance; and forming by physical vapor deposition (PVD) on the light-absorptive film an antireflection multilayer film including at least one electroconductive thin film and attenuating reflected light of incident light by interference of light.
Preferably, the PVD method comprises a sputtering method.
According to the above aspect of the present invention, there is provided a method of producing a display device of the present invention comprising the steps of: coating on a display unit displaying an image a solution containing pigment microparticles and a solvent; drying off the solvent to form a light-absorptive film containing the pigment microparticles and having a predetermined transmittance; and forming by physical vapor deposition (PVD) on the light-absorptive film an antireflection multilayer film including at least one electroconductive thin film and attenuating reflected light of the incident light by interference of light.
Preferably, the PVD method comprises a sputtering method.
According to the above method of producing the light-absorptive antireflection film of the present invention, the light-absorptive film containing pigment microparticles is formed by wet-coating and the antireflection multilayer film is formed by for example sputtering. Therefore, it is possible to produce a light-absorptive antireflection film including a light-absorptive film containing dispersed pigment microparticles and controlled in a transmittance by a simple production process at a low cost. Further, according to the method of producing a display device of the present invention, it is possible to produce a display device having the functions of prevention of reflection and decreasing spurious radiation and able to improve contrast by a simple production process at a low cost.